I google the term "Respectful Sir"

here ARE TWO sample of letter in which "Respectful Sir" were used. Sure, they both might be wrong.

A:
(http://www.clearwisdom.net/emh/articles/2004/3/21/46260.html)
The Mayor of Toledo wrote the following reply to a Falun Gong practitioner's letter:

Respectful Sir,

I carefully read your letter introducing the information about the Spanish Falun Dafa Association and the terrible situation that Falun Gong practitioners face under persecution in China.

B:
http://filmer.blogspot.com/

Dear respectful sir,

Thankyou for taking your very valluable time to answer our questions on deforestation. Your answers have been a great help.

或許Respectful 隻能同Sir連用，而不能同人名連用。